Thermally induced rearrangement of hydrogen-bonded helices in solid 4-isopropylphenol as studied by calorimetric, proton NMR, dielectric and near IR spectroscopic methods

• Published in: Chemical physics Vol. 249; no. 2; pp. 201 - 213
• Main Authors: Wójcik, G., Szostak, M.M., Misiaszek, T., Pająk, Z., Wąsicki, J., Kołodziej, H.A., Freundlich, P.
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01.11.1999
• Subjects: 4-Isopropylphenol; Hydrogen-bonded helix; Thermal; Hydrogen-bonded helix; 4-Isopropylphenol; Thermal
• ISSN: 0301-0104
• DOI: 10.1016/S0301-0104(99)00266-9

Calorimetric, dielectric and Fourier transform near infrared (IR) spectroscopic methods were used to study molecular dynamics and structural transition in solid 4-isopropylphenol (4IP) above room temperature. Pulse proton nuclear magnetic resonance (NMR) measurements were performed in the 100–340 K temperature range. A phase transition was found at 331.5 K, 1.5 K below the melting point. Energetically inequivalent methyl groups reorientations were observed in differently prepared samples and this suggested that a high-temperature polymorph occurs below the transition point as a metastable phase. Dielectric relaxation measurements showed an electric conductivity similar in value to that in water. This was detected as a pronounced contribution to the imaginary part of dielectric permittivity at temperatures higher than 310 K. Near IR spectra revealed that hydrogen bondings are stronger in the high-temperature phase than in the room-temperature-stable one. We propose that thermally induced molecular rearrangements enable proton transfer in hydrogen bonds (HBs) and this stimulates protonic conduction.